Cryptosporidium parvum is a gastrointestinal parasite capable of causing moderate to severe diarrheal disease in both humans and animals. The parasite is ubiquitous and is known to infect at least 79 different species of animals originating from more than 50 countries. Recent studies have demonstrated the presence of two high copy number, linear, double- stranded RNAs (dsRNAs) within sporozoites of 6 tested isolates of C. parvum, but not in 6 other species of the genus. Each of the DsRNAs has been purified and a library of cDNA clones representing both segments synthesized. Analysis of sequences has revealed the large segment (1786 nt) may encode and RNA-dependent RNA polymerase (RDRP), and the small segment (1374 nt) a putative protein kinase with limited similarity to mitogen-activated JNK protein kinase. No capsid protein has yet been found that co-purifies with the segments. The dsRNAs are extrachromosomal genetic element as they have no copies in the C. parvum genome, and the RDRP has an unusually high optimum temperature in vitro (50 degrees C). Investigators at Kansas State University propose to study the structure and function of the dsRNAs in C. parvum, as well as the putative proteins encoded by the dsRNA genes. Should these viral- like RNAs be found to encode proteins that modulate the parasite life- cycle, or be shown to affect the ability of the parasite to survive or induce pathogenicity, then they may also be found to represent useful therapeutic targets.